For generations, man has sought ways to harness natural kinetic resources to meet ever increasing electrical power generation needs. Notably, the implementation of large scale inland hydroelectric facilities has been amply demonstrated to be a successful method of electrical power generation. This success notwithstanding, man has yet to successfully and economically harness the natural kinetic energy contained within this planet's greatest aquatic resource--its oceans.
Successful inland hydroelectric generation has two basic requirements. First, kinetic energy must exist within a body of water. In the case of a moving flow of water such as a river, the movement of the water indicates the presence of kinetic energy. Historically, the amount of kinetic energy present in a moving flow of water has been increased by man-made structures such as dams. By accumulating a mass of water at one elevation, then releasing it to fall to a lower elevation, the extractable kinetic energy within the water flow is increased dramatically.
Apart from such man-made facilities, recent groundbreaking innovations have been made which allow extraction of kinetic energy from naturally flowing bodies of water. These innovations, which do not require large-scale construction, have opened the doors of hydroelectric generation to myriad people and places where traditional facilities are either unwanted or unfeasible.
The second basic requirement for inland hydroelectric generation is that the water must flow in one basic direction. Because inland water flow is dictated by the earth's constant gravitational pull, inland bodies of water respond to the earth's gravitational pull by flowing in a single general direction, dictated by topography. Hydroturbines have been developed for placement in such uni-directional flow which utilize hydrodynamic principles to maximize energy extraction efficiency.
In stark contrast, extraction of kinetic energy from a tidal flow poses a drastically different paradigm. Most significantly, the direction of tidal flow is largely dictated by the position of the earth with respect to other celestial bodies. As the earth rotates about its axis, as the moon circles the earth, and as the earth and moon rotate in tandem about the Sun, extra-planetary gravitational forces move oceanic tides toward shore twice each day and away from shore twice each day.
Implementation of inland-type hydroelectric generation methods and systems in such a tidal environment are impractical and inefficient. Large scale dams and other construction-intensive facilities cannot be affordably built, operated or maintained offshore. Additionally, ecological ramifications of such a project would be resoundingly negative.
For different reasons, even the newest and most innovative methods and systems for extracting kinetic energy from a natural flow of water cannot be successfully implemented offshore because of the lack of a unidirectional water flow. To be efficient, hydroturbines placed in a naturally flowing body of water rely on a continuous, unidirectional flow to create enough electrical energy to justify purchase, placement and maintenance of the devices. Additionally, such devices are designed to be hydrodynamically efficient in only a single direction of water flow. To place such devices in a body of water in which the direction of flow changes several times each 24 hour cycle substantially reduces the cost-effectiveness of this form of power generation, not to mention the lack of continuous or semi-continuous power generation.
Numerous attempts to solve this dilemma have been propounded. Most notably, a conventional hydroturbine assembly has been pivotally mounted on a structure secured to the floor of the ocean, a pier, bridge or other stationary platform. Such devices are mechanically and periodically rotated 180 degrees to face the changing direction of tidal current. While taking advantage of the power generation capability of tidal flow in both the inbound and ebb directions, these devices have failed to yield commercially feasible electrical power for several reasons. First, they require a mechanical apparatus to physically turn the hydroturbine. In salt-laden oceanic environment, devices with more mechanical parts require more maintenance and will be more costly to operate. Ultimately, devices requiring more maintenance will have less operating efficiency and a corresponding higher energy cost. Second, it is unavoidable that the pivoting movement of the hydroturbine will place weight on a load-bearing pivot point on the support structure. While deployment in saltwater provides a greater buoyancy for the device than if deployed on land or in fresh water, the point of mechanical interaction of the hydroturbine and its support structure is yet another corrosion-vulnerable location requiring, over time, expensive maintenance or replacement. Lastly, constant twisting of a slip ring to carry power to shore creates increased expense and results in less reliability than a direct, fixed interconnection.
Accordingly, a need exists for a hydroelectric turbine for tidal deployment which can utilize bidirectional tidal currents to produce electrical energy. A further need exists for bidirectional hydroturbine with does not require structural rotation or another complex mechanical apparatus to utilize tidal currents flowing in opposite directions. Yet another need exists for a bidirectional hydroturbine for deployment in tidal currents which, in addition to meeting other needs, implements recent advances in hydrodynamics to facilitate efficient conversion of kinetic energy to electrical energy.